Most definitely for a popular audience, this story of identical twins, Roger and Tony, separated as babies, now reunited and in their thirties. Roger had a chaotic and insecure childhood--bucketed from home to home, never sure of love. Tony was raised in an atmosphere of affection and warmth, and as an Italian--American and Catholic. Roger had some hit-or-miss Jewish training (the religion of his natural father with whom he lived from time to time). When the two finally met, through an intriguing series of coincidences and some detective work by Roger, their contrasting pasts offered grounds for amateur and scientific speculations having to do with the continuing controversy about the effects of environment and heredity on human behavior. Tested in adulthood by a New York psychologist, they registered amazingly similar responses in I.Q. and ""attitude"" tests, suggesting that an hereditary biological make-up influenced the results. Unfortunately, in spite of introductory remarks by Dr. Amram Scheinfeld, expert on identical twins, the actual story of Roger and Tony takes the edge off the reader's credulity, with many ""remembered"" conversations and all sentimental stops out. But in any case, a pleasantly gossipy twintype with more lay than professional appeal.